1. Field of the Invention
The present invention relates to lifting devices and more particularly to a new and useful hydraulic device especially designed for lifting a BOP from a wellhead uniformly, safely and efficiently.
2. Brief Description of the Prior Art
Prior art known to applicant from a preliminary search comprises the following United States Patents:
Owens, No. 2,661,063;
Ortloff, No. 2,897,895;
Shaffer, No. 3,241,864;
Watkins, No. 3,884,298; and
Nybo et al, No. 4,007,782.
Owens suggests to use a pair of hydraulic jacks to exert an upward force on a collar attached to pipe in a well by shearable pins which will shear when the pipe gets stuck. This causes a downward jar or jerk on the pipe, thus loosening the pipe.
Ortloff discloses a blowout device for oil wells which is characterized by a two stage seating of a clamp and the use of a sealing fluid to prevent leakage between the clamp or clamps, the housing and the pipe string. The initial seating of the clamp is secured by the application of hydraulic or pneumatic force exerted from without the assembly.
Shaffer discloses an automatic connector for oil-well drilling, casing and cementing strings. The connector includes a hollow mandrel telescopically received and adapted to be locked within a hollow barrel member, locking means carried by the barrel for locking the mandrel and barrel together, retaining means for preventing the locking means from disconnecting or releasing the barrel and mandrel elements, and unlocking means for moving the locking means away from the retaining means and for releasing the barrel from the mandrel.
Watkins discloses apparatus and method for preventing wear on a sub-sea wellhead assembly or the like wherein a BOP stack is mounted on the wellhead assembly having a string of pipe extending therethrough down into the well borehole. A plurality of rams are mounted at spaced locations on the BOP stack and movable in a direction generally normal to the central longitudinal axes of the string of pipe. Each ram carries a removable wear pad and all of the rams are movable simultaneously from a first position out of engagement with the string of pipe to a second position where the wear pads abut against and surround the string of pipe. In this manner, any wear of the string of pipe on the BOP stack is taken up by the wear pads which can be removed and replaced when necessary. In addition, drill pipe wiggle is restricted by the engagement of the pipe. Hydraulic fluid may be used to actuate the rams remotely between the first and second positions.
Nybo et al disclose a parking device for containing a BOP aboard a floating drilling station. The parking device includes a parking frame which is capable of holding the BOP with its center of gravity lying above the points at which the BOP is supported on the parking frame. The BOP can be moved as a unit back and forth between a parked position and an installed position for utilization on the drilling station. For enabling such movement a first drive mechanism is provided for raising and lowering the parking frame and additionally a second drive mechanism is provided for moving the parking frame sideways.
Prior art is also known to applicant from experience in the field.
The block-and-tackle on an oil-well drilling rig may be used to position a 20,000-70,000 lb. blowout preventer (BOP) and spacer spool on a wellhead. During drilling operations, it is sometimes necessary to lift the BOP spool assembly a foot or so above the wellhead while the block-and-tackle is in use supporting a casing string.
Conventionally, the BOP-spool assembly is lifted the required 12 to 16 inches with four or more come-alongs; at least four are required for a uniform lift; as many as eight may be required to lift a 70,000 lb. BOP. Each come-along includes a handle which must be manipulated by a worker standing on a catwalk which is usually muddy and slippery. It is not uncommon for a worker to obtain additional leverage by slipping a long length of water pipe over the come-along handle. This method of lifting a BOP is not only dangerous, but it is very time consuming. Additionally, it is difficult for the workers to manipulate the come-along handles in unison, which is essential for a uniform lift.